A modern communication system for Maharashtra police

A description is given of a system which makes use of VHF medium in the band 68-88 MHz. Fairly long distances are covered through the use of hill-top repeaters. All 29 districts are connected to the State Police HQ through a special type of radio network. For this purpose the 29 districts are divided into six groups of four to seven districts each. In a group, each district terminal is connected to every other terminal in the group. Each group is also connected to HQ through a long chain of repeaters. The system can address up to 256 terminals in the network. The system provides for point-to-point or multicast messages for up to eight stations simultaneously. The system is compatible with other carriers like VFT or voice lines on mediums such as co-axial or microwave network. Its ability to work partly on one medium and partly on another is a very useful feature. The communication protocol is outlined and the mechanism for collision detection is discussed